What’s in a Number?

How the press got the idea that food travels 1,500 miles from farm to plate.

Food critics may be finicky when it comes to celebrity chefs, but their affection for local ingredients never flags. It’s hard to open a magazine without finding an article about a photogenic farmer making handcrafted cheese or a happy family that has reduced its carbon footprint by planting a victory garden. And it seems like nearly every one of these stories offers up the same disheartening statistic to wean Americans off their penchant for industrially farmed suppers: On average, food travels 1,500 miles from farm to plate.

There’s just one problem. It’s only sort of true—and only if you live in Chicago.

The statistic was first published in 2001 when Rich Pirog, associate director of Iowa State University’s Leopold Center for Sustainable Agriculture, wanted to figure out which food distribution system—local, regional, or national—is the most environmentally friendly. To do so, he and a team of researchers looked at food miles, long a common measure in Europe. By calculating how far food traveled, they could determine the corresponding amount of carbon dioxide released into the air.

For the report, researchers examined how far 33 fruits and vegetables that had been grown in the United States traveled to a produce market in Chicago. The data, collected by the Department of Agriculture, aren’t ideal; over the last 30 years, terminal markets have declined in importance, in part because retailers like Wal-Mart manage their own distribution. In 1998, the last year data were collected, the country’s 22 terminal markets handled only 30 percent of the nation’s produce. But the data are public and therefore free to academics.

In addition to being a limited sample, terminal market data indicate only the state where the produce was grown, not what part of the state. So, for example, Pirog could have known oranges came from Florida but had no way of discerning whether they came from around Palm Beach or Orlando. For practical purposes, his team assumed that all produce came from the geographical center of each state. They then used MapQuest to determine the route a truck might take to the Chicago market. That’s a decent approximation for a high-production state like California, where crops are grown from north to south. But it’s flat-out wrong for Oklahoma, whose capital city is smack dab in the center of the state.

In the end, Pirog tallied that produce arriving in Chicago from within the United States traveled 1,518 miles. But even if you live in the Windy City, that doesn’t account for milk or meat, which make up a significant part of American diets. Nor does it account for kiwis from Italy, apples from New Zealand, or grapes from Chile. This, despite the fact that imports make up a growing percentage—15 percent of U.S. food in 2005—of what ends up on our tables.

Researchers have done little work to calculate food miles for areas outside the Midwest. A 1997 study showed that produce travels an average of 1,129 miles to Austin, 34 percent fewer than to Chicago. In 2001, an analysis of the Jessup, Md., terminal market concluded that U.S.-grown produce traveled an average of more than 1,685 miles. And though there’s no formal research to support it, Pirog says it’s safe to assume that, on average, food travels fewer miles to get to diners in California than to those in New York.

All statistics, of course, are based on a series of assumptions. And Pirog is quick to point out that whether or not the 1,500-mile figure applies to everyone and everything—or how it’s been misused—it has raised consciousness about where food comes from. It sends a message: It matters what you buy, and where you buy it. Of course, the media’s enthusiastic embrace of this statistic has as much to do with a growing sense of urgency about where food comes from as their need for quick ways to explain complex problems. Just as the fake stat that plastic takes 500 years to break down in landfills has become shorthand for America’s myopic attachment to one-time-use packaging, the 1,500 mile-figure has become a breezy way for the media to explain America’s Byzantine food system and its consequences.

There are consequences, too, for oversimplifying. If we all think in food miles, the answer is obvious: Buy local. But new studies show that in some cases it can actually be more environmentally responsible to produce food far from home. According to a 2006 report from New Zealand’s Lincoln University, it is four times more energy efficient for Londoners to buy New Zealand lamb, which is grass-fed and shipped halfway ‘round the world, than to buy lamb raised on grain in England. And if we want to combat global warming, cutting back on meat may be more effective than buying local produce.

New measures are being put in place to help guide our decisions. Pirog, for one, has moved on from food miles to studies that focus on consumer impact: Does it make sense, for example, to pick up your farm share or have it delivered? Across the Atlantic, British grocer Tesco has rolled out carbon labels that attempt to calculate the exact amount of greenhouse gases created by everything from shampoo to potato chips and fruit smoothies. Like food miles, these new numbers raise as many questions as they answer. For example, how are these carbon labels calculated? How will they stay up to date as producers change their business models to respond to rising oil prices or tax incentives for green companies? You’re more likely to get killed by a terrorist than find a simple answer.